Novel synthesis of 5,6-dihydro-4H-thieno[3,2-b]pyrrol-5-ones via the rhodium(II)-mediated wolff rearrangement of 3-(thieno-2-yl)-3-oxo-2-diazopropanoates.

[reaction: see text] Treatment of thioaryolketene S,N-acetals 12 with Hg(OAc)(2) followed by addition of 2-diazo-3-trimethylsilyloxy-3-butenoic acid alkyl esters 15 in CH(2)Cl(2) at room temperature gave 3-(3-alkylamino-5-arylthieno-2-yl)-3-oxo-2-diazopropanoates 16 in good yields. Subsequent reactions of 16 with a catalytic amount of Rh(2)(OAc)(4).2H(2)O in benzene at reflux afforded a mixture of 5,6-dihydro-4H-thieno[3,2-b]pyrrol-5-ones 18 and the corresponding enols 19 in excellent yields.